U.S. Pat. No. 5,225,130 or WO 98/40194 disclose such a process. Typically, this known process, particularly that of the WO document, provides melting and cutting the cleaned and sorted plastic material which steps can be done in an extruder followed by and cooperating with an extruder. Extruding is a typical continuous step. After this continuous step, however, both documents suggest crystallizing and condensing the material in a tumbler or similar device under vacuum in solid state.
This known process has a series of disadvantages. It is known that tumblers are often provided with a vacuuming facility so that such tumblers are the obvious device for carrying out the process. However, good sealing is a precondition, because any vacuum draws air from the environment in, especially if the seal used becomes worn out or damaged. In such a case, oxygen from air can affect the quality of the reclaimed end product.
Moreover, tumblers can only be operated in batches. This leads to the necessity of an intermediate storage facility which involves additional investment costs and the requirement of additional space. Furthermore, the production capacity of tumblers and like devices operating in batches is very limited so as to inhibit reclaiming large quantities of plastic material. Since, however, plastic material, such as PET, is increasingly in use, there is a necessity of reclaiming large quantities which cannot be done with the existing batch equipment. All these drawbacks, i.e., intermediate storage and relative small quantities handled at a necessarily high investment, result, in addition, in relative high reclaiming costs.
A further problem with PET or other plastic material to be recycled is that it may be contaminated by some chemicals which migrated in it during the former use. A typical example of such chemicals are aromatic compounds or flavors which stem from beverages or other liquids in those bottles. Another example are acids, soaps, and the like which contaminated the PET material after ordinary use. Adherents from labels have also to be removed. The prior art paid little or no attention to these factors which are relevant when it is intended that the reclaimed material should have bottle grade quality.
In this connection, reference should also be made to German patent publication No. 198 54 689, the contents of which being incorporated herein.
Several technologies are known to increase the gas barrier properties of PET packages such as bottles to reduce the ingress of oxygen or also to improve the retention of beverage carbonation. A polymer with higher gas barrier properties (e.g. PEN) or a filler which will increase the length of the diffusion path (inorganic platelets) or a substance that will react with ingressing oxygen (oxygen scavengers) might be added to the PET. This PET can now be used as a mono-material or as a layer of a multi-layer structure to manufacture the PET package. The introduction of the gas barrier increasing additive into the PET can be achieved either by producing a masterbatch, which represents an additional processing step or by direct introduction into the manufacturing process of the PET package, which adds to the complexity of the manufacturing process and requires investment in all manufacturing equipment where the additive has to be used.